Current transducer

Below you can find relevant Current Transducer information - the links will lead you to our Danisense Current Transducer range.

What is a current transducer?

What would we do without electricity? Nothing! This energy is everywhere and the ongoing energy transition and decarbonization of our industry is pulling for even more electrification in all our daily activities like e-mobility for example. Like any physical quantities if you don’t measure it, you can’t manage it! Indeed in any processes the measurement is critical to monitor, to meter and to control the system and to do it a current transducer is needed. Basically a current transducer is a device converting the current signal we wanted to measure, called “primary” current, into another signal, called “secondary” current or voltage, usable by electronic control board or instruments. As the primary current can be different (AC or DC, few mA to kA, isolated or not…), there is a large diversity of current transducers using different technologies described below.

What are the difference types of current transducers?

This chapter is describing the most popular current transducer technologies summarized in the diagram below. Basically there are two main families using either 1) the Ohm’s law (V = R I) also called “shunt” or 2) the Ampere’s law (I = ∮H ds) using the magnetic field to measure the current.

Current transducer technologies diagram

The choice of the current transducer technology is depending on the applications. The table below compares the performances between these different technologies for the main measurement parameters.

current transducer performance table

Measuring shunt

When you were student and if you remember your courses of physics, the shunt is using the famous formula V = R x I. Basically the shunt is made with a material which the resistor value is known. When a current is passing through the shunt, the resulting voltage is proportional to this current by the R factor. By using this principle we can achieve a good accuracy for AC and DC current with a small size. However, when the current is increasing (typically above 100A) it generates important heat and additionally shunts are not isolated which could be an issue for some applications with high voltages.   

Hall effect current transducers

First of all an Hall effect current transducer is using an Hall probe. Basically when you power this probe and you apply a transverse magnetic field perpendicular to the surface, it will generates a voltage proportional to this magnetic field strength. As we know from the Ampere’s law a current passing into a conductor is generating a magnetic field around. Therefore if we can concentrate this magnetic field in one specific point where the Hall probe is positioned, then we can measure the current. This is exactly what an Hall current transducer principle is doing by using a magnetic core concentrating the field in the air gap where the probe is placed. Therefore the voltage output is proportional to the magnetic field which is proportional to the primary current. The performances of the current transducer, like linearity or temperature offset drift, are strongly depending on the performances of the Hall probe in what we called Open loop configuration. To reduce this influence, the Closed loop principle has been introduced. The idea is to add a secondary winding to “reinject” an opposite proportional current to the compensate the primary current. In that case the Hall probe is always working around zero magnetic field avoiding linearity inaccuracy. Basically the performances of such Hall effect current transducers are good and most importantly isolated. However the Hall effect probe imperfection and the presence of the air gap increasing the sensitivity to the external fields make these transducers not ideal to be use for high end application like lab’s power measurement or MRI application.

Magneto-resistor (AMR or GMR)

Basically the current transducer construction is the same than for the Hall effect current transducer. However the Hall probe is replaced by a Magneto-resistor probe which the resistor value change proportionally to the magnetic field. As the Magneto-resistor is better in term of offset temperature drift these current transducers are usually more accurate than Hall effect but with the same EMC sensitivity limitation due to the air gap.

Flux Gate current transducer

In general the flux gate principle is to use an excited magnetic material coil as a probe. Thanks to a  saturation/desaturation cycle and a signal processing, this coil is able to measure proportionally the magnetic field. From that multiple options are possible to design a current transducer. It can simply replace an Hall effect probe in the air gap or the coil could have the shape of a tore. For this second option the current transducer can achieve really high accuracy (few ppm) and a strong EMC robustness. For more detail we invite you to read the detailed article on the flux gate principle.   

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